Nitrogen supplementation of ruminants grazing native pastures in New England, New South Wales

Abstract

The potential for nitrogen (N) supplementation of ruminants grazing native pastures in late winter was examined in two experiments. In experiment 1 the N contents of the diet selected by unsupplemented sheep and cattle, and by cattle receiving a supplement of linseed meal were determined. Dietary composition was not affected by supplementation but sheep selected a diet averaging 1.7 gN/100 g OM which was significantly greater than the corresponding value of 0.96 gN/100 g OM for cattle. Differences in dietary composition between sheep and cattle were also evident in experiment 2 and were confirmed by analysis of rumen liquor. It was concluded that sheep would not respond to non-protein N supplementation but that cattle might be marginally N deficient. In experiment 2 groups of heifers grazing native pasture were offered supplements of either molassesurea containing 2.54 gN/100 g OM, molasses-urea containing 7.66 gN/100 g OM, linseed meal containing 6.64 gN/100 g OM, or linseed meal treated with formaldehyde. Liveweight changes relative to an unsupplemented group were determined, and individual consumptions of supplement were measured using tritiated water. All heifers lost weight and the rate of loss was significantly greater in unsupplemented heifers than in those receiving supplement. Differences between supplemented groups were not significant after liveweight losses had been adjusted to equal energy intakes using covariance analysis.